(a) Field of the Invention
The present invention relates to a switch control device controlling a switching operation, a power supply device comprising the same, and a switch control method.
(b) Description of the Related Art
FIG. 1 is a diagram illustrating a power supply device using a buck converter. In FIG. 1, a load of the power supply device is an LED string constituted by a plurality of LEDs. In FIG. 1, a rectifying diode is implemented as a bridge diode 1.
As shown in FIG. 1, in an LED light emitting device, AC power is rectified through a bridge diode 1. The bridge diode 1 full-rectifies input AC power AC. Rectified voltage, that is, input voltage is supplied to an inductor 2 and the inductor 2 supplies driving current to the LED string depending on an operation of a power switch S. A switching unit 3 including the power switch S controls a switching operation of the power switch S.
When the power switch S is turned on, inductor current IL which flows on the inductor 2 increases and when the power switch S is turned off, the inductor current IL decreases. The maximum value of the inductor current IL depends on full-rectified voltage passing through the bridge diode 1 during one switching cycle. Accordingly, a peak value of the inductor current IL depends on a full-rectified sine wave.
A duty of the power switch S is determined depending on input voltage. Specifically, as the input voltage increases, the duty decreases and as the input voltage decreases, the duty increases. At this time, information on the input voltage is required to control the switching operation of the power switch S.
An envelop of the input voltage inputted into the power switch S that is electrically connected to the bridge diode 1 has the same phase and frequency as input voltage of a converter. Accordingly, the input voltage may be sensed by using voltage at an input terminal of the power switch S.
However, in a section where the input voltage is close to 0, the voltage at the input terminal of the power switch S is vulnerable to noise.
Therefore, a zero cross-point where the input voltage is 0 is not sensed to cause the malfunction of the power switch S.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.